A number of technologies attempt to identify the location of an object in indoor environment by estimating the distance between the devices and known beacon locations. In some such methods, a wireless device measures the received strength of wireless signals sent by multiple beacons, applies a wireless propagation model to the received signal strength values to estimate the distances between the mobile device and the beacons, and may apply a trilateration technique to the estimated distances to identify a likely location of the mobile device.
Location fingerprinting is another technique may be used for identifying location on 802.11 Wireless Local Area Networks (WLANs). A radio map of observed Signal Strength (SS) values from various locations may be obtained through a calibration process. Afterwards, proximity-matching algorithms may be used to identify location by comparing SS values observed at a wireless device to the radio map values.
However, there are many areas in indoor environments, commonly referred as “dead zones” where wireless signals are very weak or blocked such as in elevators and stairwells. In these areas neither trilateration nor fingerprinting can be effectively used to identify location.